Process of producing hard alloys



Patented July 21,1936 7 UNITED STATES 2,048,847 rnocnss or raonncmc mum armors Otto Fenssner Main, Germany,

and Alfred Jedele, Hanau-on-theassignors to the firm W. O.

Heraeus, Gwellsehaft mit bcschrinkter Haftung, Hanau-on-the-Main, Germany No Drawing. Application No. 622,568. In Germany July 14 1932, Serial July 15, 1931 5 Claims. (CL 148-13) Our invention relates to alloys which are suitable for special technical use, said alloys containing as main constituents paladium and silver. the percentage of palladium varying between 40% and 60%, while the percentage of silver varies between 20% and 48%.

Palladium-silver alloys have found some application, although to a limited extent, as a cheap substitute for platinum, for instance in connection with dental work and in the electrical industry for making contacts for small current strength, and so forth. As compared with fine silver, palladium-silver alloys are possessed of the advantage of offering a greater resistance in a chemical as well as in a mechanical respect. However, the hardness even of the hardest alloy composed of like parts of silver and palladiunr is increased to a valuewhich is about twice the value of the hardness of the two initial metals which the very soft as known- These alloys are unfit for improvement by merely a heat treatment. I

If gold is added to the palladium-silver alloys, there will result, as may be expected, an alloy of high chemical and mechanical resistance which, however, is not yet capable of beingimproved by -merely a heat treatment. 7

According to our invention, now, a fourth substance is added to the alloy, said fourth substance being usedfor hardening proper and termed herein the hardener.

Systematic investigations carried out by us have demonstrated that a number of substances which had been proposed for addition to palladium alloys do not effect an essential improvement. Such an improvement, however, may be accomplished according to our invention by means of other additional substances.

The substances which according to the present invention are used as the fourth ingredient or main hardenerare selected from the metals of the. iron group, that is Fe, Co, Ni. These hardeners may be used either individually or together, say in the form of alloys. Investigations have shown that the amount of the main hardener should not exceed 10%, and should be not less than 2%. The particular constituent, selected from the iron group, which is employed in each particular case should have the property of being dissolved by the base metal of the resulting alloy to a considerably greater degree at higher temperatures than at lower temperatures.

Of the metals of the iron groupjcobalt' and nickel deserve preference to iron. In case of alloys which are composed of about equal parts of increasing the liquidity of our invention for the amounts to 75 kg. per mm. of 16% of gold and 4% 'of nickel or of 18% of palladium and silver, cobalt and iron act both effectively as a hardene while in case of alloys which are richer in silver than in palladium,

nickel is an effective hardener, and in case of alloys which are richer in palladium than in silver, cobalt will bring about as to hardness. I

In order to have some special desirable properties preponderate or in order to suppress certain undesirable properties of the alloy, it is preferable to add a further, that is in most cases a fifth component, to the alloy in very small amounts to act also as a hardener, (hereinafter termed supplementary hardener and refining agent) The action of this supplementary hardener consists on the one hand in more or less absorbing the impurities including the gas contained better improvement in the alloy in fused condition, or in converting said impurities into slag, and on the other hand in increasing the capability of the alloy of being improved.

It is known that, for instance, phosphorus acts strongly deoxidizing and lowers the fusingpoint of the alloys of heavy metals, at the same time of the fusedv alloy. Tantalum and similar substances have become known to the modern art of alloying as being suitable for various purpose on account of their ability of absorbing gas. These substances may therefore be used with advantage in the sense purpose of. changing the properties of the alloys inone or another way.

Increase in hardness with the aforementioned alloys is due to a process of improvement by separation, that is in such a way that the alloys which have been glowed at high temperatures and chilled are soft and that the hardness is considerably increased by subsequent annealing, the

increase in hardness amounting in favorable cases to more than 100%. We have found that the most preferable temperatures for the first heating are about from 700 to 1000, and for the annealing subsequent to chilling aboutlfrom 400 to The mode of operation in making the new and technically valuable alloys of heavy metals as well as the advantages of the new alloys may be-illus-' trated by the following examples.

(a) The Brinell hardness of an alloy composed of about equal parts of silver and palladium with an addition gold and 2% of cobalt the Brinell hardness will be raised prior to the process of improvement to 100 kg. per mm and after heat treatment to from 150 to 180 kg. per mm. Also by addition of 10% of gold and 10% of cobalt'the hardness may be improved to attain a valueof 160 kg. per mm (b) An alloy composed of 60% of palladium, 20% of silver, 14% of gold, 6% of cobalt has an initial, hardness of about 110 kg. per mm The hardness is increased by heat treatment to 230 kg. per mm.

(0) An alloy composed of 40% of palladium, 48% of silver, 8% of gold, 4% of nickel after chilling from 1000 has a hardness of 115 kg. per mm and after heat treatment from 450 a hardness of 180 kg. per mm This alloy can be worked excellently.

' (d) An alloy composed of 60% of palladium,

20% of silver, 16% of gold, 4% of nickel after treatment like that stated in the Example 0 has in soft condition a hardness of 130 kg. per mm? and in hard condition of 200 kg. per mm.

The addition of about 3 to 4% of phosphorus is particularly advisable in order to reduce the fusing point of the alloy without impairing its other properties, thus facilitating the casting of the alloys, which is of particular importance when it is desired to-make castings of small dimensions, for instance, for dental purposes which castings after, final fashioning and after proper heat treatment should attain greatest possible hardness.

If the improvement process by heat treatment is united with the improvement process by case hardening which may be done in a single working step, a hardness may be obtained in the alloy eventually surpassing the above mentioned values by 100% and more.

This is due especially to the case hardening which brings about a diffusion between the several constituents of the alloy, this difiusion acting favorably upon the finely dispersed separation which is necessary for the hardening, a heavy diffusion taking place at the same time through the'crystal grid. On account of the fact that the new alloys are composed of four or more substances considerable improvements may be attained by applying the new combination of diif'erent processes of hardening, these improvements consisting essentially therein that even in the form of relatively thick fashioned pieces the completed alloys are in every case homogeneous throughout and not merely treated to a smaller or greater extent on the surface.

An especial characteristic property of the new alloys has been found to reside in the fact that within a range of temperature between 600 and 650 the structure of the alloy undergoes a con-" version, in the present case with the effect that the boundaries of the grain of the alloys will disappear more or less and by, proper treatment even 'fully and that surfaces made on the alloy by grinding will assume a uniformly chamfered appearance. As the boundaries of the grain, as known, are always more or less mechanically weak so that fractures and the like are liable to Where in the appended claims we use the expression substantially consisting of about, we

desire this to be interpreted as meaning that the,

alloys may also contain other metals of the platinum group, minor amounts of copper (which is similar to gold and does not change the tarnishresisting properties of the alloys when used in amounts up to 5%) and such substances as phosphorus or tantalum which do not materially change the properties of the alloys to be hardened by heat treatment, but do improve the alloys as to their natural hardness, melting point, liquidity, etc.

We claim: 1. The process of producing a hard alloy substantially consisting of about 60 to 40% 0!,pa1- ladium, 20 to 48% of silver, 8 to 18% of gold, and

not less than 2 nor more than 10% of a constituent selected from the metals of the'iron group (Fe, Co, Ni), which process consists in the steps of first eating the alloy to a temperature within the range of about 700 to 1000 C., chilling the alloy and reheating it to a temperature lying within the range of. about 400 to 700 C.

2. The process of producing a hard alloy sub.- stantially consisting of about 40% of palladium, 40% of silver, 16% of gold, and 4% of nickel, which process consists in the steps of first heat ing the alloy to a temperature within the range of about 700 to 1000 C., chilling the alloy and reheating. it to a temperature lying within the range of about 400 to 700 0.

3. The process'of producing a hard alloy substantially consisting ofabout 60% of palladium, 20% of silver, 14% of gold, and 6% of cobalt,

which process consists in the steps of first heating 1 the alloy to a temperature within the range of about 700 to 1000 C., chilling the alloy and reheating it to a temperature lying within the-range liquidity is increased, and the alloy is completely deoxidized by the addition of about 3 to 4% of phosphorus.

o'r'ro FEUSSNER- ALFRED JEDELE. 

